chore(api): upgrade zod to v4 with v3 compat layer (GRO-131)

- Bump zod from ^3.24.1 to ^4.3.6
- Bump @hono/zod-validator from ^0.4.3 to ^0.7.6
- Update all 12 route files to import from "zod/v3" compat layer

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/package.json

@@ -17,12 +17,12 @@
     "@groombook/db": "workspace:*",
     "@groombook/types": "workspace:*",
     "@hono/node-server": "^1.13.7",
-    "@hono/zod-validator": "^0.4.3",
+    "@hono/zod-validator": "^0.7.6",
     "better-auth": "^1.5.6",
     "hono": "^4.6.17",
     "node-cron": "^3.0.3",
     "nodemailer": "^6.9.16",
-    "zod": "^3.24.1"
+    "zod": "^4.3.6"
   },
   "devDependencies": {
     "@types/node": "^22.10.7",